Summary :
Background: Thyroid hemiagenesis is a rare congenital abnormality of the thyroid gland, resulting from failure of one thyroid lobe embryologic development. Most of the cases of thyroid hemiagenesis are euthyroid, but rarely can be asso­ciated with hyperthyroidism, hypothyroidism or malignancy. Methods and results: We report the observation of an unusual case of Basedow-Gravesí disease associated with hemiagenesis of the right lobe of the thyroid gland and left nodular goiter. Conclusions: Thyroid ultrasonography is the gold standard method for confirming the congenital anomaly but cervical scanner can be helpful. When a radical treatment is proposed, surgical option is safe with unilateral recurrent area explo­ration.